Auralex 3" Cornerfill
"CornerFills are sections of flat-cut Studiofoam corner acoustic absorbers that are beneficial in two ways. Aesthetically, they give you smooth, clean edges against which to butt your acoustic wall treatments and bass traps for a more professional appearance. Acoustically, they smooth out the excess low frequency energy that congregates in room. 3x3x24 : 16 per box (32 lineal ft.). Available colors: Charcoal, Purple, Plum, Blue, Brown, Beige, Red, Burgundy, Orange, Kelly Green, Forest Green and Teal."